Date of Award

Spring 5-7-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Jasmine Saros

Second Committee Member

Hamish Greig

Third Committee Member

Ben Peierls

Additional Committee Members

Kirk Maasch

Jeffery Stone

Abstract

Diatoms of the genus Aulacoseira are thought to bloom during enhanced lake mixing. Thus, changes in their relative abundances in lake sediment records may track lake thermal conditions and be used to reconstruct past climate. However, the lack of species-specific ecological information for the genus, and taxonomical conflicts for low-height mantle taxa, generates uncertainty about the conditions in which they occur. As many of the environmental reconstructions analyzing alpine lake sediments report species from this genus, it is relevant to understand the factors that control their growth and persistence to improve climate inferences. This research focused on low-mantle species, particularly Aulacoseira pusilla, to examine the ecology of this species in alpine lakes. By studying the distribution of this taxon in two alpine ecosystems in the Greater Yellowstone Area and testing the effect of light, nutrients, and vertical distribution in the water column, we found that light controls the distribution of the population. The nutrients availability regulates the sedimentation in stratified conditions but stimulates the growth in depleted conditions. The observation of sediment records from two alpine lakes showed that warm periods favor the relative abundance of A.pusilla. Thus, under present conditions, higher relative abundances were found in contemporary sediments. Relative abundances of this taxon were linked with low snow water equivalent, indicative of snowpack reduction or shifts in snowfall. These factors reduce lake insulation and increase radiation access. However, changes in light access did not induce the same response of similar low-mantle species. The response to deeper light access were different for A. alpigena, suggesting that there are ecological differences in the species complex and that the impact depends on the characteristics of lake water. Searching for A. pusilla in sediment records of similar lakes in the Beartooth Mountains showed that the taxon has a limited distribution in the area. However, additional studies are required. In conclusion, this study provided information about the distribution of A. pusilla in the water column, identified that light access is the principal factor regulating the growth and distribution of the taxon, and showed that changes in the relative abundance indicate reductions in snow accumulation.

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